Pigment/binder recording media, such as recording tapes, normally comprise a substrate or backing coated with a magnetizable layer containing a magnetizable pigment such as cobalt adsorbed iron oxide powder. The rest of the magnetic layer comprises a binder resin system, containing curable polymeric resins such as polyurethane and vinyl cloride/vinyl acetate/vinyl alcohol copolymer (e.g., VAGH), dispersant to help disperse the pigment uniformly within the binder, and other ingredients such as lubricant and possibly head cleaning agent (e.g., alumina powder).
Among the critical performance characteristics to be controlled in recording tapes is tape stiffness. If a tape has insufficient stiffness, it may deform or cup as it is unwound and rewound. Such deformation causes the tape not to have good flat contact with the recording and read heads or transducers of a recording or reproducing apparatus. Stiffness can be obtained by using a stiff, relatively thick substrate or backing, but as greater volumes of a recording tape are taken up by the substrate, less total tape length can be included in cassettes or cartridges, thus allowing for less total recording time. Therefore, there is a desire to reduce tape backing thickness in order to allow for greater lengths of recording tape to be included in standard cassettes. One problem which accompanies this reduction in backing thickness is that of maintaining sufficient stiffness for good recording and reproducing properties.
Electron beam curing of binder polymers for recording media magnetic layers represents a major potential advance in the state of the art of manufacturing technology for the industry. However, using conventional hydroxy-functional dispersants in electron beam cured magnetic coatings has been found to reduce stiffness of recording media. The dispersant or wetting agent for the pigment can comprise as much as 25 to 30 weight percent of the binder, and a conventional hydroxy-functional dispersant in a urethane binder system has been found to function as a plasticizer in the cured coating.